The present invention relates to a liquid heating apparatus for use in a boiler and the like utilizing an up/down flow process with respect to heated gas.
The so-called `up/down flow process` herein means a method wherein a heated gas is made to flow in an inverted U-shaped gas passage so as to effect heat exchange between the flowing heated gas and a liquid surrounding said gas passage, whereby the temperature of the heated gas is gradually lowered with its progress and the downward movement of the gas in the falling portion of the gas passage is facilitated to enhance the draft power of the passage, smooth the discharge of carbon dioxide as well as the supply of air and raise the combustion efficiency. This process will first be explained.
Referring to FIG. 1 in the appended drawings, the draft power P generating within the inverted U-shaped gas passage is expressed by the following equation: EQU P=H.multidot..DELTA.r (1)
wherein,
P: draft power (Kg/m.sup.2); PA1 H: height of gas passage (m); PA1 .DELTA.r: specific gravity of heated gas (Kg/m.sup.3). PA1 Tu: average temperature within the rising gas passage (.degree.K); PA1 Td: average temperature within the falling gas passage (.degree.K); PA1 C: constant (Kg .degree.K/m.sup.3).
When the equation (1) is altered by applying Tu and Td, it goes as follows: EQU P=H.multidot.C(1/Td-1/Tu) (2)
wherein,
As is evident from the equation (2), the more heat exchange is effected in the falling gas space, the greater becomes the value of 1/Td relative to the value of 1/Tu, and consequently the value of draft power P becomes greater. It will be understood from the above description that the draft power is closely related to the difference of density between the rising gas passage and the falling gas passage, and the greater is the difference of temperature between the rising heated gas chamber and the falling heated gas space, the greater is the draft power that is generated.
To cite an instance of the liquid heating apparatus utilizing the above described up/down flow process hitherto known, there has been proposed an apparatus such as shown in FIG. 2 by the present inventor. This previously proposed apparatus is of a structure such that an inner shell 6 is installed within an outer shell 5 by leaving a required space between the two so as to form a falling heated gas chamber 9 between them as illustrated in FIG. 2, an outside water jacket 2 is formed along the outside of this falling heated gas chamber 9, an inside water jacket 7 which communicates with the outside water jacket 2 at the upper and lower parts thereof is installed inside the falling heated gas chamber 9, a rising heated gas chamber 8 is installed within the inner shell, both chambers 8 and 9 intercommunicate by way of a flue 12 disposed at their upper parts, a flue gas exit 10 is provided at the lower part of one side of the falling heated gas chamber 9, and a water entrance 11 is provided at the lower part of one side of the outside water jacket 2 while a hot water faucet 13 is provided at the upper part of the same. In this FIG. 2, the reference numeral 14 denotes a water pipe connecting the inside water jacket 7 to the outside water jacket 2, and 3 denotes a burner for heating.
A liquid heating apparatus of such construction can admittedly generate a great draft power for the reason stated in the foregoing, but it is defective in that the water in the water jacket 2 would evaporate to increase the concentration of calcium carbonate, magnesium carbonate, etc. dissolved therein, causing deposition of such substances on the wall portion of the inner shell right above the fire chamber 17 as scale 4 in such a state as illustrated in FIG. 2. And as a result, heat exchange at this portion cannot be effected sufficiently and then crack by superheating is apt to be brought. Besides, inasmuch as the upper edge portion 15 of the water jacket 7 and the lower edge portion 16 of the falling heated gas chamber 9 are almost horizontally directed and hamper the rising of water, air separated from water becomes bubbles which attach to both edge portions 15 and 16 to cause a phenomenon of oxygen concentration cell, and corrosion is apt to take place at this portion. Moreover, inasmuch as heat exchange is efficiently effected, the low-temperature exhaust gas causes deposition of dews in the vicinity of the flue outlet 10 and the stay of the thus deposited dews results in troubles such as corrosion of the portion.
As described above, the conventional liquid heating apparatuses have been defective in that combustion loss, corrosion, etc. due to various factors would take place in every part thereof, whereby the apparatus as a whole is damaged to be dangerous for operation or unfit for prolonged use.